The present invention relates to the monitoring of vibrations occurring in components of large rotating machines, such as, for example, the bearings of turbine generators utilized in power plants.
It is known to monitor vibrations occurring in such equipment by the use of displacement, velocity and/or acceleration pickups. In order to obtain an understanding of the vibration behavior of the machine, it is also known to apply the resulting vibration signals to an analysis instrument, such as a tracking filter, a vector filter or a Fast Fourier Transform analyzer which provides detailed vibration information indicating, for example, the primary frequency and/or the amplitude of vibration of the machine, or the part being monitored. Such analysis devices are also supplied with a signal representative of the speed of rotation of the machine, which signal may be provided by a supervisory instrument associated with the machine.
It is also known that various types of information can be obtained by supplying the analyzing device with signals representing different harmonics of the basic frequency of rotation of the machine. This signal acts to tune the analyzing device. Thus, for example, if the analyzing device is tuned by a signal corresponding to the rotational speed of the machine, the vibration signal analysis will provide indications of the state of balance of the rotating components. When the signal corresponding to the rotational speed of the machine consists of one pulse per machine revolution, it is generally termed a keyphasor signal. A signal having a pulse rate different than one pulse per machine revolution will be termed herein a pseudokeyphasor signal. If the pseudokeyphasor signal corresponds to one-half the rotational speed of the machine, the analyzed vibration signals can provide information relating to conditions such as a rub condition, while a pseudokeyphasor signal corresponding to two times the rotational speed of the machine will enable the vibration signals to be analyzed in a manner to provide indications of conditions such as shaft cracking, etc. Pseudokeyphasor signals representing other harmonics or subharmonics of the rotational speed of the machine can provide other types of information relating to the operating state of the machine.
To obtain information of the desired type, the data provided by a plurality of sensors associated with the machine must be supplied simultaneously to the analyzing device together with the pseudokeyphasor signal to allow amplitude and phase comparisons to be performed.
Pseudokeyphasor signals representing various harmonics of the speed of rotation of the machine can be generated by a device such as a keyphasor multiplier/divider, devices of this type being marketed, for example, by the Bentley Nevada Company. This device is constructed to receive, from supervisory instruments of the machine being tested, a basic keyphasor signal containing one pulse per revolution of the machine and generates a reference signal having a pulse rate related to, but substantially higher than, the basic keyphasor signal.
For example, the generated reference signal may have a pulse rate 1,000 times that of the basic signal. The reference signal is then divided down to generate a pseudokeyphasor signal in the form of a pulse train having a selected pulse rate. The device includes a first manually operable control element which constitutes a multiplier for setting a selected pulse rate multiplying factor and a second manually operable control element which constitutes a divider for setting a selected pulse rate dividing factor. Both factors are integral values and serve to give the pseudokeyphasor signal pulse rate a value equal to a basic rate corresponding directly to the rate of rotation of the machine, multiplied by the multiplying factor and divided by the dividing factor.
For example, if both control elements are placed at a setting corresponding to multiplication and division factors of unity, the keyphasor multiplier/divider can be arranged to produce a pulse train consisting of one pulse for each revolution of the machine. The multiplier can be set to multiply this pulse rate by an integral value of 2, 3, etc., and the divider can be set to divide that pulse rate by an integral factor of 2, 3, etc.
In the specific multiplier/divider unit described above, each control element is a digital element producing a plural bit binary signal constituting a binary representation of the desired multiplication or division factor. Since the control elements must be set manually, their settings cannot be changed rapidly so that the tuning of the analyzing device cannot be varied at short intervals, such as would be required to obtain complete analysis data during start-up and coastdown of the machine. Moreover, if it is desired to utilize a data processing system to interpret the information provided by the analyzer, information relating to the settings of the control elements of the keyphasor multiplier/divider must be manually input to the data processing system.